This project will continue the human research on tryptamine hallucinogens begun during protocol #89-001: Human Psychopharmacology and Neuroendocrinology of DMT. The mechanisms by which N,N-Dimethyptryptamine (DMT), an endogenous tryptamine hallucinogen and Schedule I drug of abuse, exerts its biological and psychological effects. These data will have relevance to the treatment of acute and chronic hallucinogen abusers, novel treatments for endogenous psychoses (including schizophrenia) and how they may affect human mental processes.